The present invention relates to call handover in dual-mode phones.
A dual-mode phone, also called an endpoint, can accept voice/video calls from a Wi-Fi network or a cellular network. In an ideal world, the user of the dual-mode phone should be able to transition seamlessly and transparently from the cellular network to the Wi-Fi network.
In the real world, the Wi-Fi connection for the dual-mode phone is managed by a mobility controller using well known SIP and RTP protocols. SIP (Session initiation protocol) is defined for example in RFC 3261 from the IETF SIP Working Group. SIP provides for call signaling and call setup for voice over IP (VoIP) devices. The actual voice and/or video packet streams usually operate under RTP (Real-time Transport Protocol) defined for example in IETF RFC 3550.
In operation, an endpoint such as a dual-mode phone can accept or originate calls on either a cellular network or a Wi-Fi network, When the mobile endpoint is on a call using the cellular network and moves into range of the Wi-Fi network, it is desirable to switch the call to the Wi-Fi network. Similarly, when the mobile endpoint is on a call using the Wi-Fi network and moves out of range of the Wi-Fi network, it is desirable to hand the call off to the cellular network. The problem is to manage these transitions minimizing delay, dropped packets, and duplications of packets during connection handover.